The present invention relates to a flat spring structure for magnetic tape cassettes, in particular video cassettes.
As is known, in video cassettes flat springs are currently used which engage with the pivots provided at the axis of rotation of the tape supporting reels.
In conventional embodiments, the flat springs are associated at their middle portion with the inner surface of the cover and act, by elastic pressure contact, on said pivots at the free ends of said flat springs.
The flat springs are currently manufactured according the most widely varying configurations starting from the elongated rhomboidal configuration to more recent configurations which substantially have an extension with a more reduced width.
In all the embodiments currently available on the market said flat springs, seen edgewise, have a substantially curved or piecewise configuration with the concavity facing towards the supporting reels.
Flat springs, according to universally adopted standards, must have such a shape as to exert on the reel, at the moment of their use, an elastic thrust at the contact pivot, which can be estimated, for example for the VHS system, at approximately 200 g.
With the known described arrangement, since the action and reaction points are merely constituted by the pivots for contact with the end of the lamina and by the central portion of the lamina itself, which is connected to the cover, from the point of view of the static calculation of forces, a force is exerted on the cover, at the point of contact with the lamina, which is directed towards the outside of the cover of the cassette and is equal to the sum of the two forces exerted on the lamina at the pivots, that is to say, an outwardly directed thrust is exerted on the cassette, in a point located in the central portion, which for example for the VHS system is approximately 400 g.
Calculating the various moments, the maximum resisting moment is located at the point of contact with the cassette, that is to say in the central region of the elastic lamina, and decreases to 0 at the region of contact with the pivot.
This arrangement of the forces causes the need to currently use springs which have a high elastic constant so that, from a constructive point of view, one must use laminae which have a relatively large width and thickness, with consequent considerable consumption of material for their manufacture.